/Engine/Source/Runtime/Engine/Public/SceneView.h
Method to know the maximum value that can be returned by GetPrimaryResolutionFraction_RenderThread(). Can be called on game or rendering thread. This should return >= 1 if screen percentage show flag is disabled.
[DynamicRenderScaling::TMap](API\Runtime\RenderCore\TMap)< float > GetResolutionFractionsUpperBound() const